In the CS digital broadcast available since 1995 and the BS digital broadcast available since Dec. 1, 2000 in Japan, a transport stream (TS), in which image information, audio information and additional information appended to the informations such as program information obtained by compressing digital information are multiplexed according to the MPEG2 system standard, is digitally modulated and transmitted to a broadcast station. A digital broadcast receiver separates the image, audio and other informations from the transport stream (TS) obtained by digitally demodulating a received signal and reproduces them. Such a digital broadcast receiver is increasingly widespread.
Thus, the multiplexed data such as the image and audio in the digital broadcast is transmitted via the transport stream (TS) which is a data string having a fixed length generally called a transport stream packet (TSP).
FIG. 20 is a schematic view of a general format of the transport stream packet (TSP). The transport stream packet (TSP) is a packet having the fixed length of 188 bytes, in which initial four bytes are specifically called a packet header. The first byte is a synchronizing byte for synchronizing with a processing device for processing the transport stream packet (TSP), in which a data value is constantly “47h” (h denotes a hexadecimal number). Subsequent to the first byte, a transport error indicator (TEI) bit for indicating “1” when a data error is detected in a demodulating circuit, a payload unit start indicator (PUSI) for indicating the presence of a leading position of a section or a packaged elementary stream (PES) packet, a transport scramble control (TSC) bit for indicating scramble information of the TSP, an AFC bit for indicating the presence/absence of an adaptation field, a continuity counter (CC) for indicating a packet continuity, and the like, are assigned.
The fifth byte and thereafter are comprised of an adaptation field of a variable length (N bytes) and a payload of a variable length (188-4-N bytes). The payload area stores the PES packet including the image, audio and subtitle, information for identifying a recipient, various service information and the like.
The TSP received in the digital broadcast receiver is filtered in order to retrieve only necessary data, and the data which is scrambled so that the data can be viewed/listened by particular subscribers is descrambled and then outputted. As examples of a destination of the output, a memory accessible by a CPU, an AV decoder for retrieving the audio/image, and the like, can be mentioned. An apparatus, which filters and descrambles the TSP to thereby retrieve the desired data as in the described manner, is called a transport stream separating apparatus.
The conventional transport stream separating apparatus is constituted in the manner that all of the processing steps for separating the transport stream, such as the PID filtering and descrambling, are executed by means of the hardware. As other possible constitutions of the apparatus, all of the processing steps for separating the transport stream could be executed by means of the software, or the processing steps could be executed separately on the hardware and the software in such manner that the PID filtering and descrambling are executed on the hardware and the section filtering and CRC check are executed on the software.
Examples of the transport stream separating apparatus for executing all of a plurality of processing steps for the transport stream separation by the hardware are disclosed in No. H10-341419, No. 2000-13448 (P2000-13448A) and No. H11-239186 of the Publication of the Unexamined Japanese Patent Applications. An example of the transport stream separating apparatus for dividing the plurality of processing steps for the transport stream separation between the hardware and software is disclosed in No. H10-210461 of the Publication of the Unexamined Japanese Patent Applications.
When a plurality of processing steps for the transport stream separation is entirely executed on the hardware, a high operation frequency and additional circuits are demanded in order to deal with all of possible circumstances and statuses (for example, real-time processing of a plurality of multi-sections, multiple-type scrambling method and the like). On the other hand, when the plurality of processing steps is executed on the software, a high power for the CPU is constantly required. In the case of the constitution in which the processing steps are divided, a maximum performance may not be exerted if the processing steps are divided in a fixed manner.
For example, FIG. 23 shows a processing-time correlation in the case of processing N number of multi-sections in a conventional technology. A total time length for the section filtering is increased as the number of the multi-sections is increased. Further, if a time point when the hardware completes the section filtering process goes beyond a time point when the TSP to be processed next arrives, a real time performance of the transport stream separating process cannot be guaranteed. In order to solve the problem, it was conventionally necessary to modify the constitution such as improving the operation frequency to shorten the processing time, additionally providing a buffer for temporarily memorizing any TSP which cannot be processed in time, and the like.